Preheat oven to 350°F and line two baking sheets with parchment paper.
Melt 1 cup of chocolate chips with butter cubes in microwave, stirring in 30 second increments until melted. Set aside to cool.
Whisk together flour, cocoa, baking powder, and salt in a medium bowl, set aside
Using mixer, mix together the eggs, sugars, and vanilla in a large mixer bowl on medium-high speed for 5 minutes.
Reduce speed to low and beat in melted chocolate for 1 minute.
Add flour mixture and mix on low speed, just until combined for 20 seconds or so.
Fold in chocolate chips. Cookie dough will resemble a gooey brownie batter.
Use a medium cookie scoop coated lightly with nonstick spray. Drop the cookies on the baking sheets, spacing cookies 3 inches apart. Cookies will spread, so allow room.
Bake for 14 minutes, until tops shiny, crackly looking.
Remove from oven and sprinkle with flaky salt, if desired.
Let cookies cool for 5-10 minutes on baking sheets, then transfer to a wire rack to cool completely.
Store cookies in an airtight container at room temperature for 1-2 days.
One batch makes 18-20 cookies.